A variety of recent studies suggest that apes know what other individuals do and do not see. The results of each study may be explained by postulating some behavioural rule that individuals have learned that does not involve an understanding of seeing. The patchiness of coverage gives this kind of explanation a very ad hoc feeling, especially since there is rarely any concrete evidence that animals actually have had the requisite experiences to learn the behavioural rule – there is just a theoretical possibility. It is thus more plausible to hypothesize that apes really do know what others do and do not see in many circumstances.